The Organic Light Emitting Display (OLED) Element possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The structure of the OLED display element generally comprises: a substrate, an anode, a cathode and an organic function layer sandwiched between the anode and the cathode. The organic function layer generally comprises a Hole Transport Layer (HTL), an Emissive Layer (EML), and an Electron Transport Layer (ETL). Each function layer can be one layer, or more than one layer. For instance, the Hole Transport Layer can be subdivided into a Hole Injection Layer (HIL) and a Hole Transporting Layer; the Electron Transport Layer can be subdivided into an Electron Transporting Layer and an Electron Injection Layer (EIL). The principle of the OLED is that the illumination generates due to the carrier injection and recombination under the electric field driving of the semiconductor material and the organic semiconductor illuminating material.
Generally, the manufacture method of the OLED display element is forming an anode on the substrate, and forming a Hole Transport Layer on the anode, and forming an Emissive Layer on the Hole Transport Layer, and forming an Electron Transport Layer on the Emissive Layer, and forming a cathode on the Electron Transport Layer, wherein material of the cathode and the anode generally utilizes the Indium Tin Oxide (ITO). The manufacture of the function layers of HTL, EML, ETL generally includes two kinds, the Vacuum Thermal Evaporation and the Ink-jet Print (IJP).
In the manufacture of organic function layer of the AMOLED element, the Ink-jet Print has advantages of material saving, mild process condition, more uniform film formation, and thus possesses more application potentials. IJP is to directly drop coat the ink with OLED material into the pre made pixel definition layer, and the required pattern is formed after the solvent is evaporated. The pixel definition layer comprises a dam, and a plurality of grooves formed by the dam surrounding and aligned in array. The grooves are employed to restrain the ink, and with drying and baking, the ink shrinks in the area restricted by the grooves and the thin films are formed. Because the OLED light emitting material has many layers, and the hydrophilic-hydrophobic properties of the inks employed for all layers are different. As printing the different OLED layers, the requirements to the hydrophilic-hydrophobic properties of the dam lateral sides are different. For the hydrophobic ink, it requires that the dam lateral side possesses a certain hydrophily to prevent that the contact angle is over large to result in the thinner edge film thickness; vice versa, for the hydrophilic ink, it requires that the dam lateral side possesses a certain hydrophoby to prevent that the contact angle is over small to result in the thicker edge film thickness. On the other sides, the upper surface of the dam generally needs to be hydrophobic to avoid the remain of the ink to make the ink all flow into the groove. However, it is very difficult to achieve the aforesaid objective with only one material to manufacture the dam.